This invention relates to fabricating III-V semiconductor devices and, in particular, to a structure and method for bonding and electrically contacting semiconductor devices.
In the fabrication of III-V semiconductor lasers, the bonding of the device chips to suitable heat sinks or conductors and subsequent wire bonding to make electrical contact to the device are critical steps. Typically, the device is solder-bonded to an outside surface such as a heat sink or conducting pad by use of a preform comprising a metal such as In. The opposite surface of the device is then typically wire bonded to establish an ohmic contact to that surface.
In one particular example, the p-surface of an AlGaAs laser included layers of titanium and platinum over the contact to the p-type surface and a thick Au pad formed selectively over the platinum layer. This surface was bonded to a heat sink by means of an indium preform and a liquid flux including Zn and HCl. The opposite (n-type) surface included a layer of Ge-Au alloy which in some cases covered a selective area of the n-surface defined by an opening in an SiO.sub.2 layer. An ohmic contact was provided to this surface by soldering a wire to the Ge-Au layer (see Swaminathan et al., "Bonding Pad Induced Stresses in (AlGa)As Double Heterostructure Lasers," Journal of Applied Physics, Vol. 54, p. 3763 (b 1983)).
While prior art bonding and electrical contact methods produced reliable devices, the procedures were time-consuming and required a high degree of operator skill. It would be more efficient, for example, to provide a wire contact to a surface by means of ultrasonic bonding techniques and, further, to provide bonding of the other surface with a fluxless preform bonding procedure, which is generally cleaner than a system using flux. Furthermore, in view of the various applications for a particular laser chip, it is desirable to provide a contact metallization which allows either major surface to be bonded to an appropriate outside surface while the opposite device surface can be chemically contacted. During the solder-bonding of either surface, it is also necessary to prevent the solder from flowing along the sides of the chip and causing short circuiting of the junction. It is therefore desirable to include in the metallization some means for stemming the flow of solder metal to the edges of the major surfaces of the chip.
It is therefore an object of the invention to provide a metallization and a bonding procedure with the above-described desirable features.